This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Spiders have been using protein-based nanomaterials that have the ability to self-assemble into fibers and sheets for over 450 million years. However, it is only in the past 15 years that we have started to understand the basis for these amazing materials. Biological polymers and assemblies, such as spider silk, are typically long, helical, fibrous structures. The components of these fibrous-assemblies are difficult to crystallize, since their natural tendency is to form fibers. Spider dragline silks have extremely unsurpassed mechanical strength, a combination of very high elasticity and tensile strength. A knowledge of the micro-structure of the silk fibers is crucial in understanding the factors deciding on these unique mechanical properties. This knowledge about its structure would help understanding the structure-property relationship and inturn enable it to be used as new smart bio-materials, for numerous applications ranging from airbags to sensors to micro-sutures to artificial ligaments and tendons to drug delivery coatings. Fiber diffraction is the only practical method of structure determination at the molecular level for these assemblies. The difference between fibers and crystals is that, in fibers, the molecules are parallel to each other (as they are in crystals), but they are randomly rotated about the long axis of the fiber. As a result, the data obtained from an x-ray fiber diffraction experiment are cylindrically averaged relative to the data that would be obtained from a hypothetical crystal of the same aggregate.